Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to fluid measurements, more particularly, to an instrument for measuring the viscosity of fluids.
2. Description of the Related Art
It has been known that the viscoelasticity, or tackiness, of some bodily fluids change in response to bodily rhythms. For example, the cervical mucus and saliva of a female has a maximum fluidity just before ovulation, where ovulation is defined as the moment that an ovum is released from the follicle. This knowledge led to the applicant""s previous activities in the development of techniques for monitoring the viscoelasticity, or tackiness, and other properties of cervical mucus and saliva as predictors of time of ovulation and to improvements in rheometer or viscometer apparatus for measuring such viscoelastic properties. See, for example, L. E. Kopito and H. J. Kosasky, xe2x80x9cThe Tackiness Rheometer Determination of the Viscoelasticity of Cervical Mucus,xe2x80x9d Human Ovulation, edited by E. S. E. Hafez, Elsevier, North-Holland Biomedical Press, 1979, pp. 351 et seq., S. S. Davis, xe2x80x9cSaliva is Viscoelasticxe2x80x9d, Experientia, 26:1298, (1970), R. H. Davis et al., xe2x80x9cSaliva Viscosity Reflects the Time of Ovulationxe2x80x9d, Experientia, 30:911, (1974), and U.S. Pat. Nos. 4,002,056 and 4,167,110.
It is also known that the normal viscoelasticity of some bodily fluids changes in response to abnormal body conditions. For example, in a newborn baby with cystic fibrosis, the meconium, the first bowel movement of a newborn, has a viscoelasticity approximately five times that of a baby without cystic fibrosis.
There are a number of devices available for measuring viscosity. The above-identified U.S. Pat. No. 4,779,627, in addition to disclosing a process for determining female ovulation time by measuring saliva viscoelasticity, discloses a device for measuring the viscoelasticity of the sublingual saliva. The device has a shape somewhat like a syringe, with an outer cup, an inner cup concentric with and located within the outer cup, and a plunger. A roughened surface on the end of the plunger holds the saliva sample. The plunger is inserted into the inner cup until the saliva sample is compressed against the bottom of the inner cup. A predetermined amount of weight pulls the inner cup downward, stretching the saliva sample. If the viscoelasticity of the saliva is low, the saliva sample will fracture, causing the inner cup to fall to the bottom of the outer cup. An indicator at the bottom of the outer cup indicates that the inner cup has fallen to the bottom, which, in turn, indicates that ovulation will soon take place. If, however, the viscoelasticity of the saliva is high, the saliva sample will hold the plunger and inner cup together so that the inner cup will not fall to the bottom, indicating that ovulation will not take place in the near future.
The main disadvantage of the device is that it must be taken apart in order to take a sample. The plunger must be removed from the inner cup before being inserted in the mouth to obtain a saliva sample. This has the potential for the person to easily contaminate the saliva sample by incorrectly reinserting the plunger after taking the sample, invalidating the measurement.
U.S. Pat. Nos. 5,640,968, 5,851,190, and 6,149,604 disclose handheld instruments for measuring saliva viscoelasticity. The instruments are designed specifically for saliva, which means that their range of measurement is very limited, and cannot measure the viscosity or viscoelasticity of dense fluids such as meconium.
An object of the present invention is to provide an instrument that can measure a wide range of viscosities and viscoelasticities.
The viscosity and viscoelasticity measuring instrument of the present invention includes a housing within which the measuring mechanism resides. The components of the measuring mechanism include a cam, a follower arm, a spring, and a plate fixture. The cam is a vertical, circular disk with a spiral slot that is rotated by an electric stepper motor. A cam follower attached to the follower arm resides in the spiral slot so that, as the cam rotates, the follower arm pivots upwardly or downwardly about its fixed end. The spring is a flat, preferably metallic, strip, one end of which is attached to and collinear with the fixed end of the follower arm. Thus, the spring pivots in the opposite direction as the follower arm. The plate fixture holds a removable plate assembly that has three components, a lower plate, an upper plate, and a plate clip. The two plate components have mating sample surfaces on which the fluid to be tested is placed. The fixture has a lower jaw pivotally attached to the instrument base and an upper jaw pivotally attached to the free end of the spring. The pivoting attachments allow the plate sample surfaces to align as they come together during a test. The jaws have channels for receiving and holding the plates.
To perform a measurement, a fluid is placed on the lower sample surface. The cam rotates, pushing the free end of the follower arm upwardly, causing the follower arm to pivot about its fixed end. The spring, attached to the fixed end of the follower arm, rotates downwardly, pressing the sample surfaces of the upper and lower plates together. Then the cam is reversed, causing the spring to impart a separation force on the plates. The amount of time it takes for the plates to separate is measured and converted to a viscosity value. A strain gauge mounted to the spring indicates when the plates separate.
Other objects of the present invention will become apparent in light of the following drawings and detailed description of the invention.